Gmail is great for record keeping of parent communication and student communication. We use an online curriculum in my classroom. After initially checking student work, it would take an insurmountable amount of time to check for newly completed work each day. Students are responsible for notifying me of their now completed missing or incomplete work. The Gmail provides a record for both student and teacher of work completion.
In my capacity as a high school guidance counselor, I use Gmail as a system for tracking parent / guardian questions and activities. Parents receive information about school activities, especially career events, via Gmail communiques.